PURPOSE: To dispense with the monitoring or 'no sheet supply' and enable a large amount of data to be printed out without printing interruption halfway through operation by detecting the remaining amount of the sheets to be fed to a printer using a computer, and indicating 'no sheet supply' without printing out data, if the detected value is lower than the required number of sheets for an output from a printer.

CONSTITUTION: A sensor 4 which detects the remaining amount of the sheets is provided on a sheet case 3. If a request for an output to a printer 2 generates, a computer 1 loads an output from the sensor 4 to detect a remaining sheet amount. At the same time, the computer 1 calculates the number of sheets required for a file as a purpose of printer output, and causes a display part 5 to indicate a remaining sheet shortage without allowing data to be printed out, if such a shortage occurs. Then the computer prompts an operator to interpret whether an output from a printer should be permitted. Thus the monitoring of 'no sheet supply' is no longer required and even a large amount of data can be printed out without interrupting printing halfway through operation.